Department of Environmental Affairs and Development Planning Sea Level Rise and Flood Risk Assessment for a Select Disaster Prone Area Along the Western Cape Coast Phase B: Overberg District Municipality Phase 3 Report: Overberg District Municipality Sea Level Rise and Flood Hazard Risk Assessment Final March 2012 REPORT TITLE : Phase 3 Report: Overberg District Municipality Sea Level Rise and Flood Hazard Risk Assessment CLIENT : Provincial Government of the Western Cape Department of Environmental Affairs and Development Planning: Strategic Environmental Management PROJECT : Sea Level Rise and Flood Risk Assessment for a Select Disaster Prone Area Along the Western Cape Coast. Phase B: Overberg District Municipality AUTHORS : D. Blake : REPORT STATUS Final REPORT NUMBER : 790/3/2/2012 DATE : March 2012 APPROVED BY : S. Imrie D. Blake Project Manager Task Leader This report is to be referred to in bibliographies as: Department of Environmental Affairs and Development Planning. (2011). Sea Level Rise and Flood Risk Assessment for a Select Disaster Prone Area Along the Western Cape Coast. Phase B: Overberg District Municipality. Phase 3 Report: Overberg District Municipality Sea Level Rise and Flood Hazard Risk Assessment. Prepared by Umvoto Africa (Pty) Ltd for the Provincial Government of the Western Cape Department of Environmental Affairs and Development Planning: Strategic Environmental Management (March 2012). Phase 3: Overberg DM Sea Level Rise and Flood Hazard Risk Assessment 2012 EXECUTIVE SUMMARY INTRODUCTION Umvoto Africa (Pty) Ltd was appointed by the Western Cape Department of Environmental Affairs and Development Planning (DEA&DP) to undertake a sea level rise and flood risk assessment for a select disaster prone area along the Western Cape coast. The Phase B assessment area was defined as the Western Cape coastline within the Overberg District Municipality (DM), from Blousteen at Kogel Bay (at the boundary of the City of Cape Town) to Infanta near the Breede River mouth (at the district municipal boundary with the Eden DM). The Western Cape DEA&DP required that a literature assessment of current global and local understanding and knowledge with regards to climate change and sea level rise be undertaken, in association with the development of a sea level rise and flood inundation Geographic Information System (GIS) model for this project. Umvoto Africa proposed a three-phase work approach, namely: Phase 1 – Inception and Data Acquisition, Phase 2 – GIS Model Development, and Phase 3 – Risk Assessment. This report describes the coastal hazard risk assessment undertaken during Phase 3. COASTAL HAZARD RISK ASSESSMENT METHODOLOGY For this study, the Overberg DM coastline was subdivided into 24 sections, termed Coastal Zone Management Units (CZMUs). The risk of each CZMU to three coastal hazards was qualitatively assessed using a modified version of the rapid risk assessment methodology described in Blake and Hartnady (2009). The three coastal hazard types that were selected in order to undertake the West Coast DM coastal risk assessment were sea level rise induced coastal erosion and inundation, groundwater contamination from saltwater intrusion (as a result of sea level rise) and extreme coastal events (storm surges, estuarine flooding and tsunamis). The risk of each CZMU to each specific hazard can be determined by using the classic risk equation, where Risk (R) = (Hazard (H) x Vulnerability (V)) / Coping Capacity (C). Hazard, vulnerability and coping capacity were in turn scored from 1 to 5 (with 1 representing very low and 5 representing very high) for each CZMU for each hazard, allowing the risk to be calculated. Hazard scores for each CZMU were calculated by determining the severity and probability of each specific hazard. Severity and hazard were both given a score out of 5 based. The equation Hazard (H) = (Probability (P) + Severity (S)) / 2 was then used to calculate a final hazard score out of 5. Vulnerability (V) was divided into three types, namely social (So), environmental (En) and economic (Ec) vulnerability. Social vulnerability was based on the possible amount of human deaths, economic vulnerability on the total approximate economic cost in Rands, and environmental vulnerability on the possible environmental damage to a specific ecosystem (i.e. whether sensitive/protected or not) that may result from a specified hazard or disaster. Each vulnerability type was scored out of 5 based on the variables, and a final vulnerability score was calculated using the equation V = (En + Ec + So) / 3. Coping capacity defines the resilience a community or area has to a disaster i.e. to what extent will a community be affected by and how long it will take to recover from a disaster. Each CZMU was given a coping capacity score for each hazard, based on the implementation of the various stages of the Hyogo Framework for Action (HFA): Priorities for Action. The HFA priority areas strive to reduce the impact of disasters through gender sensitive disaster preparedness and risk reduction i.e. by increasing the coping capacity. Executive Summary Page i Phase 3: Overberg DM Sea Level Rise and Flood Hazard Risk Assessment 2012 Each HFA priority area was given a score out of 5, depending on whether there was none to very limited implementation (1), limited implementation (2), partially implemented (3), mainly implemented (4) and fully implemented (5). The final coping capacity was then calculated using the equation: C = (HFA1 + HFA2 + HFA3 + HFA4 + HFA5) / 5. Full implementation of all the HFA priority areas will result in a CZMU having a high coping capacity, ensuring that it is able to deal with coastal disasters. Little to no implementation of the HFA priority areas will result in coastal communities within the CZMU being highly affected by and taking a long period of time to recover from coastal disasters. The CZMUs along the Overberg DM coastline have low coping capacities, due to minor implementation of the HFA priority areas. HFA1 is the highest scoring priority area, due to the development of national, provincial, and in some cases local coastal legislation, policies and frameworks to deal with ICZM and coastal hazards. Little to no implementation of HFAs 2 to 5 has occurred across the entire Overberg DM coastline however. The risk equation of R = H x V / C shows that coping capacity has a significant influence on the final risk assessment, and hence the importance in developing coping capacity mechanisms to deal with disasters in order to reduce the final risk e.g. even if a specific CZMU had the highest H x V ranking possible of 25, a coping capacity of 5 (i.e. full implementation of all five HFA priority areas) would reduce the risk of the CZMU to that hazard or possible disaster to 5 (moderate risk). The benefit of strong coping capacity is highlighted with regards to possible groundwater contamination at Hermanus, where strong monitoring systems and public awareness/participation have reduced the risk of saltwater intrusion. COASTAL HAZARD RISK ASSESSMENT RESULTS The majority of the Overberg DM CZMUs are at a low risk to sea level rise induced coastal erosion and inundation (58% of total CZMUs), with the remaining CZMUs at moderate risk (predominantly the stretch from Pearly Beach to De Hoop Vlei). The regions most at risk (although still at moderate risk) include sandy coastal sections linked with larger estuaries (Bot River, Klein River and Walker Bay CZMUs), and the coastal stretch between Pearly Beach and De Hoop Vlei (with the exception of rockier coastal areas at Aasvontein and Ryspunt). The areas of low risk reflect moderate to high gradient coastal areas, often with rocky coastlines or high backing coastal dune systems, with relatively little development in lower elevation areas or within the coastal foredune. Areas of moderate risk in turn reflect relatively low gradient coastal areas, often with extensive beaches or large estuaries, in association with areas of development (or possible future development) close to the shoreline. The majority of the Overberg CZMUs are at a low risk to groundwater contamination from salt water intrusion related to sea level rise (58% of total CZMUs), with the exception being the Overstrand (Vermont to Kleinbaai, moderate risk) and Cape Agulhas/Struisbaai regions (moderate to high risk). The at risk areas of the Overberg DM are comprised of hydraulically conductive and therefore vulnerable primary (Bredasdorp Group) and fractured quartzitic (Peninsula and Skurweberg Formation) aquifers, which are used to a large extent for groundwater supply in towns such as Hermanus and Struisbaai. Vulnerability and risk may increase over time, due to possible future potable water shortages in the area as a result of climate change, and the associated increased exploitation of groundwater resources. The introduction of real time telemetry monitoring, in association with aquifer wellfield modelling and regional ecological and groundwater monitoring, can reduce the risk of over abstraction and salt water intrusion, as evidenced by the monitor-model-manage approach employed in Hermanus for the abstraction of groundwater from the coastal Peninsula Formation aquifer. Executive Summary Page ii Phase 3: Overberg DM Sea Level Rise and Flood Hazard Risk Assessment 2012 The majority of the Overberg DM CZMUs are at a low (46% of total CZMUs) to moderate (50% of total CZMUs) risk from extreme coastal events such as large storm surges and tsunamis. The regions at most risk include the relatively low gradient sandy and rocky coastal sections of Struisbaai (focused wave energy north of the harbour), Quoin Point (direct exposure of the fishing community of Buffeljagsbaai to large swell), Cape Agulhas and Vermont-Sandbaai (large proportion of shore fronting properties close to the high water mark), Klein River and Bot River (estuarine systems prone to flooding). The areas of low to moderate risk reflect moderate to high gradient coastal areas, often with rocky coastlines or high backing coastal dune systems, with relatively little development in lower elevation areas or within the coastal foredune e.g.